The present disclosure relates to an image forming apparatus which heats and pressurizes a toner image to fix the toner image on a paper sheet.
In an image forming apparatus such as a printer, jam of a paper sheet may occur. When occurrence of jam is detected, a printing operation such as paper sheet conveyance is stopped in order to avoid worsening of the jam. However, at the stop of the paper sheet conveyance, if a paper sheet which carries a toner image stops at a fixing portion, the quality of an image formed later may be reduced, or melted toner may be attached to a component of the fixing portion. Thus, there is an image forming apparatus in which when paper sheet conveyance is stopped due to occurrence of jam, a paper sheet is conveyed until passing through a fixing portion, in order to prevent the paper sheet from stopping at the fixing portion.
For example, an image forming apparatus is known which includes: a first fixing portion which fixes a toner image at a first nip region; a second fixing portion which performs fixing on a recording material, on which the fixing has been performed by the first fixing portion, at a second nip region again; a recording material detection portion which determines whether the recording material contacts with the first nip region or the second nip region; a conveyance abnormality detection portion which detects whether abnormality of conveyance of the recording material occurs at the downstream side in a recording material conveying direction as seen from the position of the second fixing portion; and a conveyance control portion which causes the recording material to be conveyed toward the downstream side in the recording material conveying direction and stopped at a position at which the recording material does not contact with the first nip region and the second nip region, when the conveyance abnormality detection portion detects occurrence of conveyance abnormality and the recording material contacts with the first nip region or the second nip region. The image forming apparatus attempts to avoid deterioration of image quality which is caused due to offset or the like at occurrence of conveyance abnormality.
When paper sheet conveyance is continued in a state where a paper sheet is jammed, it may be difficult to remove the paper sheet due to the paper sheet being jammed in a compressed manner, etc. In addition, when a severely jammed paper sheet is forcibly removed, a component within the apparatus may be broken, or it may be difficult to remove a part of the paper sheet due to the paper sheet being torn, whereby much time and labor are taken to handle the jam. Thus, in the image forming apparatus, when occurrence of jam is detected, paper sheet conveyance is stopped.
Here, at the fixing portion which fixes a toner image on a paper sheet, the paper sheet is passed through a nip formed between a heating rotator and a pressure rotator. To pressurize the paper sheet, the pressure rotator is pressed against the heating rotator. Thus, when paper sheet conveyance is stopped due to occurrence of jam, it is difficult to pull out and remove a paper sheet caught by the nip of the fixing portion.
Therefore, as in the image forming apparatus, when paper sheet conveyance is stopped due to occurrence of jam, a paper sheet may be conveyed such that the paper sheet does not remain at the fixing portion.
However, in the image forming apparatus, when jam has occurred, even though other paper sheet is present at the downstream side of a paper sheet that is passing through the fixing portion, the paper sheet is conveyed from the fixing portion toward the downstream side. Thus, the paper sheet discharged from the fixing portion may collide against the other paper sheet at the downstream side which has been stopped due to the occurrence of jam. In addition, the other paper sheet that has been stopped due to the occurrence of jam and is present at the downstream side of the fixing portion becomes an obstacle, and thus a paper sheet that is passing through the fixing portion at the occurrence of jam may not be completely discharged from the fixing portion. Moreover, when the paper sheets collide against each other, it may be difficult to remove the paper sheets from a sheet conveyance path, or the paper sheets may be bent.
As described above, in the image forming apparatus, when paper sheet conveyance is stopped due to occurrence of jam, conveyance of a paper sheet from the fixing portion may be stopped after the paper sheet is discharged from the nip of the fixing portion. However, when jam has occurred, since a paper sheet is conveyed to the downstream side in a paper sheet conveying direction without consideration of the distance between sheets in order to pass the paper sheet through the fixing portion, an adverse effect may occur such as collision of the paper sheet against a preceding paper sheet or difficulty in removing the paper sheet from the sheet conveyance path.
The image forming apparatus includes the two fixing portions. When jam has occurred at a cutting portion located at a downstream end in the paper sheet conveyance direction, a paper sheet is conveyed toward the downstream side such that the paper sheet does not contact with each fixing portion. However, in order to prevent collision of paper sheets, the size of each paper sheet needs to be limited to a small size. In addition, in order to support large-sized paper sheets, the intervals among the first fixing portion, the second fixing portion, and the cutting portion need to be sufficiently large, and thus there is the demerit that the image forming apparatus is considerably increased in size.